The dumping of hazardous wastes and toxic chemicals into the environment is an on-going problem both here in the United States and throughout the world. In the United States alone, superfund sites are numerous and Environmental Protection Agency regulations have been enacted that require those responsible for such contaminated areas to clean them up. Gasoline and other petroleum products are discharged into the soil on a regular basis both inadvertently and deliberately. There is an unquestionable need for means to remediate areas containing high levels of inorganic and organic solvents, PCBs, volatile hydrocarbons and the like.
U.S. Pat. No. 4,202,282 to Hobbs discloses a method for thermally processing materials in a chamber on a conveyer belt utilizing infrared heating to drive off gasses from the material being processed, and mixing the released gasses with air flowing over, above, and parallel to the materials in the opposite direction of the material movement to provide a portion of heat for drying the materials. Apparently the materials are wet at the time they are introduced to the incinerating chamber.
U.S. Pat. No. 4,670,634 to Bridges et al. teaches in situ decontamination of soil utilizing radio frequency energy whereby the contaminants are vaporized, the gases removed from the sample and late r cooled and condensed. The process then collects the removed hydrocarbons in fluid form.
U.S. Pat. No. 4,815,398 to Keating et al. discloses an apparatus for drying contaminated material to below the cracking temperature of the volatile organics which contaminate the material, followed by heating in a kiln to a temperature high enough to break down the volatile organics to non-toxic products, and recovering the gaseous products.
U.S. Pat. No. 4,881,475 to De Leur et al. discloses a method for cleaning contaminated soil by indirectly heating the soil in a sealed rotating furnace, then combusting the released contaminants in a second furnace. In this process, the heat is provided to the soil by induction from the furnace wall rather than being applied directly to the soil.
U.S. Pat. No. 4,974,528 to Barcell discloses yet another decontamination apparatus consisting of a rotary dryer in which contaminated soil is exposed to a gaseous flame to vaporize the contaminants. Air is then mixed with the released volatiles to form an exhaust gas which is filtered, heated and incinerated at less than 1700.degree. F.
U.S. Pat. No. 5,514,189 to Crosby teaches a method and apparatus for soil remediation comprising a thermal desorption unit in which contaminated soil is heated under a vacuum thereby vaporizing the contaminants. The contaminants are drawn through a discharge pipe wherein they are condensed by cooling. The gases are condensed to a liquid and contained in a recovery vessel. The soil is then recycled back to the location from which it was removed.
U.S. Pat. No. 5,553,189 to Stegmaier discloses a radiant heating plate for the treatment of contaminated surfaces. The apparatus further comprises an insulating layer and a vapor barrier that is positioned above the heating plate and below the insulation. The heating plate heats the contaminated surface which vaporizes the volatile hydrocarbons, inorganic toxins, etc. These are then drawn up through a thermal oxidizer and collected in an absorbent bed downstream from the heating plate.
None of the aforementioned patents disclose methods or means to decontaminate polluted soil in large quantities using a batch process that can remediate toxic soil samples in a safe, efficient manner. A related patent to the present application, Reissue of U.S. Pat. No. 5,127,343 now Re 36,222 to O'Ham discloses and claims a method and apparatus for the revival of contaminants from the soil consisting of a shallow container with vertical sides and a bottom with a plurality of recessed chambers contained therein. An open mesh entry area is at one end and a gas discharge orifice exists at the other end of each of the recessed chambers contained therein. A rack consisting of burners or heating elements slides over and covers the bin for heating the soil sample to be treated. The soil is heated under reduced pressure so that volatile hydrocarbons and other inorganic or organic contaminants are vaporized as a gas. The reduced pressure is created by a vacuum in the base-contained chambers and this pulls the toxic gases downwardly through the soil and out through the chambers for discharge and removal.